The present invention relates, in general, to removing contaminants. More specifically, the present invention relates to a method and apparatus for removing contaminants from a semiconductor mold through sublimable particles.
Semiconductor encapsulation molds are typically used to encapsulate semiconductor packages. This is typically accomplished by transfer molding thermosetting plastic compositions to form the semiconductor packages. In addition to traditional epoxy resins, new resin compositions, named ‘green compounds’, have been introduced as alternatives. The green compounds are chosen over the traditional resins, as they do not contain halogens and are eco-friendly. In comparison to the traditional resins, the green compounds are stickier, and cause sticking to the mold surface and staining of packages so formed. This leads to the formation of stresses in the internal parts of the molded packages during ejection from the mold surface. This, in turn, reduces the strength of the molded package. This eventually gives rise to quality and reliability issues, such as chip crack, micro crack, moisture seepage, etc. In order to achieve higher molding quality, the encapsulation molds are required to be cleaned frequently to get rid of the oxidized release agents and any other contaminants. Moreover, the frequency of cleaning required for the green compound is more than thrice that for the traditional resins.
Various techniques, such as scraping, media blasting, melamine cleaning, rubber cleaning, plasma cleaning, laser cleaning and chemical cleaning, have been employed for removing contaminants from a base surface of a mold. However, each of these techniques suffers from one or more disadvantages. Some of these techniques are not very delicate and can often cause damage to the base surface. In other cases, thin flashes and burrs are left on the base surface, thereby creating defects in the mold. In certain techniques, the mold has to be taken out from a machine on which the mold was mounted, and has to be disassembled and cleaned part-by-part. Removing and remounting the mold back onto the machine take a lot of time and fine tuning, thereby leading to wastage of time. Some of these techniques involve spillage of media particles that needs to be removed properly from various parts of the mold, so that the mold can be assembled precisely. Any leftover particle may cause inaccurate assembling of the parts, thereby damaging the mold when put to use. Most of these techniques produce a huge amount of waste products that are not eco-friendly. Disposal of these waste products is another hassle. Some of these techniques include an outgassing process, which produces fumes that pollute semiconductor materials being used for molding and a clean work environment.
In light of the foregoing discussion, there is a need for a method and apparatus for removing contaminants from a semiconductor mold that does not damage the semiconductor mold, can be performed inline, reduces the time required to clean, and reduces ecologically unfriendly waste.